• Coupled systems mechanics
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• 제8권4호
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• pp.351-375
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• 2019

The present work investigates the use of a rigid rocking block as a tool to reduce vibrations in a frame structure. The study is based on a simplified model composed by a 2-DOF linear system, meant to represent a general M-DOF frame structure, coupled with a rocking rigid block through a linear visco-elastic device, which connects only the lower part of the 2-DOF system. The possibility to restrain the block directly to the ground, by means of a second visco-elastic device, is investigated as well. The dynamic response of the model under an harmonic base excitation is then analysed in order to evaluate the effectiveness of the coupling in reducing the displacements and the drift of the 2-DOF system. The nonlinear equations of motion of the coupled assemblage 2-DOF-block are obtained by a Lagrangian approach and then numerically integrated considering some reference mechanical and geometrical quantities as variable parameters. It follows an extensive parametric analysis, whose results are summarized through behaviour maps, which portray the ratio between the maximum displacements and drifts of the system, with and without the coupling with the rigid block, for several combinations of system's parameters. When the ratio of the displacements is less than unity, the coupling is considered effective. Results show that the presence of the rocking rigid block improves the dynamics of the system in large ranges of the characterizing parameters.

• Structural Engineering and Mechanics
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• 제18권2호
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• pp.231-246
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• 2004

In this paper, a comparison of various random vibration and deterministic dynamic analyses of cable-stayed bridges subjected to asynchronous ground motion is presented. Different random vibration methods are included to determine the dynamic behaviour of a cable-stayed bridge for various ground motion wave velocities. As a numerical example the Jindo Bridge located in South Korea is chosen and a 413 DOF mathematical model is employed for this bridge. The results obtained from a spectral analysis approach are compared with those of two random vibration based response spectrum methods and a deterministic method. The analyses suggest that the structural responses usually show important amplifications depending on the decreasing ground motion wave velocities.

• 한국지진공학회논문집
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• 제26권3호
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• pp.117-125
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• 2022

In this study, centrifuge model tests were performed to evaluate the seismic response of multi-DOF structures with shallow foundations. Also, elastic time history analysis on the fixed-base model was performed and compared with the experimental results. As a result of the centrifuge model test, earthquake amplification at the fundamental vibration frequency of the soil (= 2.44 Hz) affected the third vibration mode frequency (= 2.50 Hz) of the long-period structure and the first vibration mode (= 2.27 Hz) of the short-period structure. The shallow foundation lengthened the periods of the structures by 14-20% compared to the fixed base condition. The response spectrum of acceleration measured at the shallow foundation was smaller than that of free-field motion due to the foundation damping effect. The ultimate moment capacity of the soil-foundation system limited the dynamic responses of the multi-DOF structures. Therefore, the considerations on period lengthening, foundation damping, and ultimate moment capacity of the soil-foundation system might improve the seismic design of the multi-DOF building structures.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2010년도 춘계학술대회 논문집
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• pp.1478-1485
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• 2010

In this paper, the nonlinear dynamic response of Vehicle-Bridge interaction with the coupled equations of motion including nonlinear Hertzian contact is presented. The moving train model is chosen to have 10 degrees of freedom (DOF). The bridge is modeled as 2D Euler-Bernoulli beam element with 4 DOF for each element, two for rotations and another two for translations. The nonlinear Hertzian contact is used to simulate the interaction between vehicle and bridge. Base on the relationship of wheel displacement of the vehicle and the vertical displacement of the bridge in Hertzian contact, the coupled equations of motion of the whole system is derived. The convenient formulation was encoded into a computer program. The contact forces, contact area and stress of the rail surface were also computed. The accuracy and efficiency of the proposed program are verified and compared with exact analytical solution and other previous studies. Various numerical examples and parametric studies have demonstrated the versatility and applicability of the proposed program.

• 로봇학회논문지
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• 제6권3호
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• pp.263-273
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• 2011

This paper analyzes the motion of a horseback riding robot which has two actuators and three joints. It is impossible to control the saddle to get to any position and orientation using the two motors because the robot has less degrees of freedom than the number of joints. Therefore it is required to know the possible location and orientation along with the velocity characteristics of each pose prior to motion planning. For this purpose, this paper analyzes the characteristics of the robot motion. The authors derive the forward and inverse kinematics of the robot motion and developed the trajectory editor for motion planning. Also, Jacobian of the robot is analyzed. It reveals that one of the actuator has little influence to the speed of the saddle motion while the other affects the speed of the saddle motion dominantly. The approach of the paper can be applied for the analysis of characteristics of a robot which has less number of actuators than that of joints.

• 한국전산구조공학회논문집
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• 제24권2호
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• pp.167-175
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• 2011

본 연구에서는 속도의 변화 그리고 모델링방법이 자기부상열차의 주행성에 미치는 영향을 파악하는데 목적을 두고 있다. 이를 위하여 2000:1의 처짐비를 가지는 동일한 교량 위를 속도를 변화시키면서(100km/h에서 700km/h까지 100km/h간격으로) 6가지 모델의 자기부상열차를 주행시키기 위하여 4자유도 6자유도 10자유도 차량에 대한 운동방정식을 구성하고 4계 룬지쿠타법을 적용하여 수치해석을 수행한다. 해석결과를 보면 속도가 낮을수록 보기 및 EMS의 개수가 많은 모델일 수록 자기부상열차의 주행성이 향상됨을 알 수 있다.

• 제어로봇시스템학회논문지
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• 제20권8호
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• pp.875-881
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• 2014

The redundancy resolution of the seven DOF (Degree of Freedom) upper limb exoskeleton is key to the synchronous motion between a robot and a human user. According to the seven DOF human arm model, positioning and orientating the wrist can be completed by multiple arm configurations that results in the non-unique solution to the inverse kinematics. This paper presents analysis on the kinematic and dynamic aspect of the human arm movement and its effect on the redundancy resolution of the seven DOF human arm model. The redundancy of the arm is expressed mathematically by defining the swivel angle. The final form of swivel angle can be represented as a linear combination of two different swivel angles achieved by optimizing two cost functions based on kinematic and dynamic criteria. The kinematic criterion is to maximize the projection of the longest principal axis of the manipulability ellipsoid of the human arm on the vector connecting the wrist and the virtual target on the head region. The dynamic criterion is to minimize the mechanical work done in the joint space for each of two consecutive points along the task space trajectory. The contribution of each criterion on the redundancy was verified by the post processing of experimental data collected with a motion capture system. Results indicate that the bimodal redundancy resolution approach improved the accuracy of the predicted swivel angle. Statistical testing of the dynamic constraint contribution shows that under moderate speeds and no load, the dynamic component of the human arm is not dominant, and it is enough to resolve the redundancy without dynamic constraint for the realtime application.

• 한국정밀공학회지
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• 제29권1호
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• pp.64-71
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• 2012

In this paper, a parallel manipulator is comprised of two sliders and four links. Sliders execute a linear reciprocating motion depending on parallel guides and make the connected links rotate. A couple of links connected by sliders do coupling motion. The end-effector called a link tip has orientation angle. Through the kinematics analysis of this manipulator, we found displacement, velocity and acceleration using direct and inverse kinematics. We used equations that derived from this analysis and determined five constraint conditions. These conditions had much to do with rotation states of links, the relative relation of link length and coupling motion state. To verify those, we suggest a new algorithm regarding constraint conditions of a manipulator. With the result which performed the algorithm, we found out that operation range of coupled links was limited by relative relation of link length and that manipulator was not able to carry out a series of link motion, in case of being the link vertical between two parallel guides.

• 한국정밀공학회지
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• 제31권10호
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• pp.897-904
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• 2014

In this paper, two-DOF parallel manipulator has the sliders which execute a linear reciprocating motion depending on parallel guides and the end-effector which can be adjusted arbitrarily. To investigate the dynamic characteristics of the manipulator, the dynamic performance index is used. The index is able to be obtained by the relation between the Jacobian matrix and the inertia matrix. The kinematic and the dynamic analysis find these matrices. Also, the dynamic model of the manipulator is derived from the Lagrange formula. This model represents complicated nonlinear equations of motion. With the simulation results of the dynamic characteristic of the manipulator, we find that the dynamic performance index is based on the selection of the ranges for the continuous movement of the manipulator and the dynamic model derived can be used to the control algorithm development of the manipulator.

• 한국정밀공학회지
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• 제22권11호
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• pp.182-189
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• 2005

The human knee joint is the intermediate joint of the lower limb that is the largest and most complex joint in the body. Understanding of joint-articulating surface motion is essential for the joint wear, stability, mobility, degeneration, determination of proper diagnosis and so on. However, many studies analyzed the passive motion of the lower limb because of the skin marker artefact and some studies described medial and lateral condyle of a femur as a simple sphere due to the complexity of geometry. Thus, in this paper, we constructed a three-dimensional geometric model of the human knee from the geometry of its anatomical structures using non-uniform B-spline surface fitting as a study for the kinematic analysis of more realistic human knee model. In addition, we developed and verified 6-DOF contact model of the human knee joint using $C^2$ continuous surface of the inferior region of a femur, considering the relative motion of shank to thigh during locomotion.